1. Field of the Invention
This invention regards a method of positioning a power tong at a pipe joint. More particularly, it regards a method of positioning a power tong at the pipe joint of a pipe, where, after the pipe joint has been brought within the working area of a power tong, the power tong must be displaced to a position that corresponds with that of the pipe joint. A camera which may be displaced in parallel with the pipe, and which is linked to a display, is displaced until the image of the pipe joint coincides with a marker. A signal is then transmitted to a control, indicating that the power tong is to be displaced to a position that coincides with the camera and thereby the pipe joint. Preferably, the control, which receives information about the relative positions of the camera and the power tong, is programmed to guide the power tong to said position. The invention also regards a device for implementation of the method.
2. Description of the Related Art
When screwing together and unscrewing pipe strings, e.g. in connection with drilling in the ground, power tongs are typically used for the actual screwing operation. The positioning of the power tong, which in addition to the actual power tong also comprises a backup tong, at the pipe joint must be relatively accurate to avoid damage to the pipe couplings, and to ensure the success of the screwing operation.
A pipe string may for instance consist of drill pipes or casing. In this context, the term pipes also includes other equipment such as drill collars or tool components that are commonly connected into a pipe string.
According to prior art, the power tong is guided to the correct position by an operator near the power tong. It is also known to place sensors by the pipe string, the sensors being arranged to indicate to position of the pipe joint, so that the power tong can then automatically be guided to the correct position.
US document 2005/0104583 describes an apparatus for positioning pipe joints by means of so-called eddy current. Position measuring by use of an eddy current field will only provide an approximate position report, due to the relatively “blurred” change in the eddy current field at the approach of the pipe joint.
Safety reasons dictate that preferably, personnel should not be present on the drill floor during the operations in question. Furthermore, sensors have turned out not to be capable of indicating the position of the pipe joint with sufficient accuracy. The reason for this is, among other things, that the sensors can hardly take into account the fact that the pipe components have been repaired or for other reasons have different dimensions.
The object of the invention is to remedy or reduce at least one of the drawbacks of prior art.
The object is achieved in accordance with the invention, by the features stated in the description below and in the following claims.